Abstract

Abstract A series of tests with four tufted ducks Aythya fuligula, feeding on freshwater mussels Dreissena polymorpha was performed to test the hypothesis that tufted ducks select sub-optimal mussel sizes to avoid the risk of taking items that are too large to be swallowed, or at least, have highly variable profitabilities. The results indicate that the largest mussel size class available influenced the overall pattern of selection and that an increasing risk of taking unprofitable mussels caused a decrease in mean mussel size eaten. Some of the recorded differences between the birds tested could be explained by differences in the shape of the profitability curves for each individual.

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